Study On Nonlinear Seepage Law Of Gas In Goaf Based On Continuous Expansion Coefficient Model

Gas is the main hazard in thecoal mine safety production.With the improvement of the production capacity of the coal mining face and the acceleration of the speed of the working face,the gas emission will be increased.The technology of high drained roadway drainage is one of the effective means of regional gas control in coal mines.Because of its long drainage time and high drainage rate,the drainage system is simple and easy to manage.It has become the main way to solve the problem of gas overrun in high gas and spontaneous combustion coal seam.Based on the S2107 working face of 3# coal seam in Yu Wu Coal Mine and the study of the evolution of the mining fissures and the gas migration,this paper uses theoretical research and numerical simulation method to study the reasonable level layout of high drainage roadway in goaf,and the main conclusions are as follows:(1)According to the goaf overburden fracture evolution law,through the FLAC3 D numerical simulation software to establish the S2107 model of the model along the working face,the working face advancing direction for 5 times and 5 times respectively from excavation,excavation of overburden strata of different section of plastic failure and stress distribution nephogram analysis research.The "two belts" through in-depth analysis of the scope of section nephogram and empirical formula: range above the goaf roof distance within 23 m for caving zone,fractured zone for the range of 22m-49 m.(2)Due to the particularity of coal mine underground environment,with the continuous advancing of working face,the fluid flow field caused by destruction,deformation and failure of overburden strata in goaf is complicated.Based on the "O" type circle theory,the goaf is simplified scientifically and rationally,and the numerical simulation model of the ladder type is established.On the basis of previous studies,the continuity equation,the momentum conservation equation and the component transport equation are used.The RNG k-epsilon model is used to establish a turbulent calculation model for gas flow in the fractured zone.In order to achieve continuous dilatation coefficient of porous media in goaf,the empirical formula of parameters and dilatation coefficient in porous media under nonlinear flow conditions is obtained through the relationship between porosity and coefficient of expansion.The distribution function of the dilatation coefficient is programmed by C language in Visual Studio.At the same time,the empirical formula is compiled into the program language,and the C language is imported into FLUENT through UDF interface,so that the gob model with non-uniform continuous dilatation coefficient can be obtained.(3)The degree of compaction and permeability in different regions of the goaf are different,and the gas seepage mechanism in different regions of the goaf is different.The FLUENT simulation software is used to simulate the gas migration law in goaf under different flow of gas fluid in goaf.The simulation shows that compared with nonlinear seepage,linear seepage has larger gas concentration in goaf,and the initial air leakage is smaller.The closer to the goaf,the faster the air leakage curve decays.(4)The law of gas nonlinear seepage in the "U" ventilation system with different wind speeds is compared.With the increase of the inlet wind speed,the air leakage in the goaf is increased,and the gas concentration in the upper corner is reduced from 12% to 7%,which is more than the coal mine safety regulations.The gas concentration in the deep area of the goaf increases with the increase of air leakage.In order to ensure the air volume of the working face and the gas concentration in the upper corner,it is necessary to set up high pumping for gas extraction.(5)The extraction of pressure gas from high pumping roadway not only solves the overlimit of gas in the working face,but also reduces the gas emission in the adjacent coal seam.This paper uses the FLUENT numerical simulation,and according to the coal seam roof of different vertical distance,the distance of return airway at different distances,to get the reasonable position parameters of high pumping lane for the vertical distance is 34 m,the horizontal distance is 32 m,high pumping Lane pure gas drainage amount is larger,the extraction rate is high,the working surface of the gas concentration at in the corner of the "coal mine safety regulations",U type ventilation + high drainage roadway drainage system can make the upper corner gas concentration is reduced to below 1%,to ensure that the working face can be safe and efficient production.(6)In order to ensure the high drainage roadway gas drainage effect,changes in the way the wind speed and high pumping lane and return air roadway than two parameters.The gas purity and the gas concentration in the upper corner of the working face are different with the change of the wind speed and the extraction ratio.The optimum intake wind speed is 2m/s,and the optimum drainage ratio is 1:5.(7)Through the measurement of S2107 working face in 3# coal seam of Yu Wu coal industry,the data of gas extraction and gas extraction are obtained.The actual measured height drainage flow,gas concentration and gas concentration in the upper corner are observed and analyzed in the field.With the continuous development of the cracks in the overlying strata,the amount of gas extracted from the high drainage roadway gradually increases,and the upper corner gas concentration decreases.The application of high drainage roadway drainage system is conducive to the safe production of the working face,improving the utilization rate of gas,to a certain extent,solving the gas overrun of the working face and improving the economic benefits.